The invention relates to a device for the pneumatic injection of fuel into a cylinder of an internal combustion engine and more particularly, but not exclusively, a pneumatic injection device for a two-stroke engine.
Two-stroke engines are known having one or more cylinders with, associated with each of the cylinders, a pneumatic fuel injection device for atomizing a liquid fuel by means of a pressurized gas which is generally compressed air and feeding the carburetted mixture obtained into the cylinder of the engine. The cylinder is fed with and swept by the fresh air independently of the pneumatic fuel injection which is initiated at a given time during the operating cycle of the engine.
The pneumatic fuel injection device comprises a chamber which may be placed in communication with the inner chamber of the cylinder through at least one valve controlled by a cam. The injection chamber is fed with pressurized gas which may come either from an auxiliary reservoir or from a part of the engine producing this pressurized gas.
In particular, it has been proposed to feed the injection device with compressed air from a capacity which is recharged by the pump housing providing the fresh air supply and scavenging of the cylinder of the engine.
In the case of high power engines, the amounts of fuel injected into the cylinder are very considerable and require either a high amplitude lift of the valve placing the injection chamber in communication with the cylinder, or the use of a large diameter valve. By high power engine is meant more particularly engines delivering more than 25 to 30 kW per cylinder.
In the case of very large engines, it is not possible to increase the diameter of the valves beyond a certain limit, since the inertia of the valve then becomes excessive. Similarly, it is not possible to increase the lift amplitude or time beyond a certain limit.
In the case of large engines, it has been proposed to divide the injection device of each of the cylinders into two, using two valves and two liquid fuel injectors per cylinder. The drawbacks of this approach are however that the cost price of the engine is considerably increased and its adjustment is delicate.